1. Field of the Invention
This invention relates to a composite mechanism multi-axis machine tool and particularly to a multi-axis machine tool that combines a conventional orthogonal coordinate feeding axis mechanism and a parallel type spatial linkage mechanism for providing at least five dimensional axes movement.
2. Description of the Prior Art
Conventional orthogonal coordinate multi-axis machine tool (referring to FIG. 1 for a traditional three axes linear feeding machine tool as an example) has three feeding axes located respectively in three mutually orthogonal cantilever beams (such as X, Y, Z axes in FIG. 1). One axis is laid upon the other serially. The tolerance and feeding inertia of the main spindle is generally large and difficult to control because it is an aggregate of its own tolerance and inertia at Z-axis plus the tolerance and inertia of X and Y axes feeding members. The rigidity and precision of the main spindle 1 is thus suffered.
Another conventional orthogonal coordinate five-axis machine tool has three mutually orthogonal linear feeding axes and two rotating feeding axes. The linear feeding axes are serially laid upon one another. There are a variety of configurations for the two rotating axes. However they also are laid upon one another serially. It is bulky and high cost to fabricate. Inertia impact is difficult to alleviate. The rigidity and displacement acceleration problem at the main spindle 1 also are problems without effective solution.
In order to address aforesaid problems, there are improvements being made by some machine tools manufacturers. For instance, Geodetic Co., and Gidding & Lewis Co., have disclosed various types of Hexapod multi-axis machine tools. Ingersoll Co., has disclosed an octahedral machine tool frame under U.S. Pat. No. 5,259,710. They all try to use multiple parallel linkages mechanism to replace traditional orthogonal coordinate machine tool design to reduce inertia and tolerance accumulation effect, and to improve main spindle rigidity and machining acceleration between the cutter and the workpiece.
However some of the problems of aforesaid prior arts still remain, notably the followings:
1. the hexapod parallel type spatial linkage mechanism mostly uses ball joint. The fabrication techniques for high precision, high rigidity and large moving an angular ball joint still do not reach perfect level. Its service life and strength is also much lower than conventional bearing type rotation joint. PA1 2. The fabrication, assembly and tuning of hexapod parallel type spatial linkage mechanism need very high degree of precision. The tuning work is done in a three-dimension space and is radically different from the traditional tuning work which is done on a plane. The tuning variables for hexapod linkage are many and difficult to control. PA1 3. When there is a need for large movement angle of rotation axis for the machine tool, total orientational workspace for a hexapod parallel type linkage mechanism becomes very small. It is also difficult to make the orientational workspace a cubic square. PA1 4. The orientational workspace might have singular points. To calculate the singular point and try to avoid it will significantly increase design difficulty. PA1 5. The controller for a hexapod parallel type spatial linkage mechanism is a control system with multiple input and output variables in nonlinear nature. It is a complex system, takes long time to design and is expensive.